Extension tube tips and tricks

Couldn't find "search" so pardon if this question has already been posed elsewhere in the forum...

I have the two kits lenses that came with the camera. Santa brought me a 35mm f/1.8G DX lens for Christmas, as well as a set of Kenko extension tubes (set of three in 12, 20 and 36mm, which can be used singularly or in combination with each other for different focal lengths).

I've been doing some research and sort of understand the plusses and minuses of using them, such as having to make allowances for some extra light in some cases. I'm going to have to play around a bit and find that practical experience.